The present embodiments relate to a high-voltage final stage.
In the case of modern X-ray tubes, the position of the beam and the quality of the beam are varied by magnetic or electric fields. Use has mostly been made for variable focus size and focus position of a system of magnets, and the electron beam is blocked by electric fields. If these electrodes are to take over the function of the magnetic system, one is to be provided with a voltage source that may provide a constant focusing voltage and a rapidly alterable deflecting voltage.
Due to the high accelerating voltage, a deflecting voltage of several kilovolts is to be provided, and this may not be built up using typical linear transistor final stages each having one transistor per output polarity. For deflection of the beam in both directions, the final stage is to supply a bipolar voltage. For the purpose of setting the working point, a cross current is to be avoided because of the power losses that result with these high voltages. The final stage is to be designed for a capacitive load.
In the prior art, a bipolar voltage multiplier cascade, for example, is a known way of producing the deflection voltages. However, the cascade with capacitors and diodes limits the maximum current, and hence the dynamics. Use is also made of low-voltage final stages, the output signals from which are transformed to a high voltage by a transformer. The conversion ratio of the transformer drops at low frequencies, and the transformer may not produce DC voltages. Also known are bipolar high-voltage switched-mode regulators, the output signal from which is filtered. These have a residual ripple that is interfering in many applications.